[PATCH 3/3] powerpc/mm/hash: Avoid multiple HPT resize-downs on memory hotunplug
From: Leonardo Bras
Date: Fri Mar 12 2021 - 02:33:10 EST
During memory hotunplug, after each LMB is removed, the HPT may be
resized-down if it would map a max of 4 times the current amount of memory.
(2 shifts, due to introduced histeresis)
It usually is not an issue, but it can take a lot of time if HPT
resizing-down fails. This happens because resize-down failures
usually repeat at each LMB removal, until there are no more bolted entries
conflict, which can take a while to happen.
This can be solved by doing a single HPT resize at the end of memory
hotunplug, after all requested entries are removed.
To make this happen, it's necessary to temporarily disable all HPT
resize-downs before hotunplug, re-enable them after hotunplug ends,
and then resize-down HPT to the current memory size.
As an example, hotunplugging 256GB from a 385GB guest took 621s without
this patch, and 100s after applied.
Signed-off-by: Leonardo Bras <leobras.c@xxxxxxxxx>
---
arch/powerpc/include/asm/book3s/64/hash.h | 2 ++
arch/powerpc/include/asm/sparsemem.h | 2 ++
arch/powerpc/mm/book3s64/hash_utils.c | 28 +++++++++++++++++++
arch/powerpc/mm/book3s64/pgtable.c | 12 ++++++++
.../platforms/pseries/hotplug-memory.c | 16 +++++++++++
5 files changed, 60 insertions(+)
diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h
index 843b0a178590..f92697c107f7 100644
--- a/arch/powerpc/include/asm/book3s/64/hash.h
+++ b/arch/powerpc/include/asm/book3s/64/hash.h
@@ -256,6 +256,8 @@ int hash__create_section_mapping(unsigned long start, unsigned long end,
int hash__remove_section_mapping(unsigned long start, unsigned long end);
void hash_memory_batch_expand_prepare(unsigned long newsize);
+void hash_memory_batch_shrink_begin(void);
+void hash_memory_batch_shrink_end(void);
#endif /* !__ASSEMBLY__ */
#endif /* __KERNEL__ */
diff --git a/arch/powerpc/include/asm/sparsemem.h b/arch/powerpc/include/asm/sparsemem.h
index 16b5f5300c84..a7a8a0d070fc 100644
--- a/arch/powerpc/include/asm/sparsemem.h
+++ b/arch/powerpc/include/asm/sparsemem.h
@@ -18,6 +18,8 @@ extern int memory_add_physaddr_to_nid(u64 start);
#define memory_add_physaddr_to_nid memory_add_physaddr_to_nid
void memory_batch_expand_prepare(unsigned long newsize);
+void memory_batch_shrink_begin(void);
+void memory_batch_shrink_end(void);
#ifdef CONFIG_NUMA
extern int hot_add_scn_to_nid(unsigned long scn_addr);
diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index 1f6aa0bf27e7..e16f207de8e4 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -794,6 +794,9 @@ static unsigned long __init htab_get_table_size(void)
}
#ifdef CONFIG_MEMORY_HOTPLUG
+
+atomic_t hpt_resize_disable = ATOMIC_INIT(0);
+
static int resize_hpt_for_hotplug(unsigned long new_mem_size, bool shrinking)
{
unsigned target_hpt_shift;
@@ -805,6 +808,10 @@ static int resize_hpt_for_hotplug(unsigned long new_mem_size, bool shrinking)
if (shrinking) {
+ /* When batch removing entries, only resizes HPT at the end. */
+ if (atomic_read_acquire(&hpt_resize_disable))
+ return 0;
+
/*
* To avoid lots of HPT resizes if memory size is fluctuating
* across a boundary, we deliberately have some hysterisis
@@ -872,6 +879,27 @@ void hash_memory_batch_expand_prepare(unsigned long newsize)
pr_warn("Hash collision while resizing HPT\n");
}
}
+
+void hash_memory_batch_shrink_begin(void)
+{
+ /* Disable HPT resize-down during hot-unplug */
+ atomic_set_release(&hpt_resize_disable, 1);
+}
+
+void hash_memory_batch_shrink_end(void)
+{
+ unsigned long newsize;
+
+ /* Re-enables HPT resize-down after hot-unplug */
+ atomic_set_release(&hpt_resize_disable, 0);
+
+ newsize = memblock_phys_mem_size();
+ /* Resize to smallest SHIFT possible */
+ while (resize_hpt_for_hotplug(newsize, true) == -ENOSPC) {
+ newsize *= 2;
+ pr_warn("Hash collision while resizing HPT\n");
+ }
+}
#endif /* CONFIG_MEMORY_HOTPLUG */
static void __init hash_init_partition_table(phys_addr_t hash_table,
diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c
index f1cd8af0f67f..e01681e22e00 100644
--- a/arch/powerpc/mm/book3s64/pgtable.c
+++ b/arch/powerpc/mm/book3s64/pgtable.c
@@ -199,6 +199,18 @@ void memory_batch_expand_prepare(unsigned long newsize)
if (!radix_enabled())
hash_memory_batch_expand_prepare(newsize);
}
+
+void memory_batch_shrink_begin(void)
+{
+ if (!radix_enabled())
+ hash_memory_batch_shrink_begin();
+}
+
+void memory_batch_shrink_end(void)
+{
+ if (!radix_enabled())
+ hash_memory_batch_shrink_end();
+}
#endif /* CONFIG_MEMORY_HOTPLUG */
void __init mmu_partition_table_init(void)
diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
index 353c71249214..9182fb5b5c01 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -425,6 +425,8 @@ static int dlpar_memory_remove_by_count(u32 lmbs_to_remove)
return -EINVAL;
}
+ memory_batch_shrink_begin();
+
for_each_drmem_lmb(lmb) {
rc = dlpar_remove_lmb(lmb);
if (rc)
@@ -470,6 +472,8 @@ static int dlpar_memory_remove_by_count(u32 lmbs_to_remove)
rc = 0;
}
+ memory_batch_shrink_end();
+
return rc;
}
@@ -481,6 +485,8 @@ static int dlpar_memory_remove_by_index(u32 drc_index)
pr_debug("Attempting to hot-remove LMB, drc index %x\n", drc_index);
+ memory_batch_shrink_begin();
+
lmb_found = 0;
for_each_drmem_lmb(lmb) {
if (lmb->drc_index == drc_index) {
@@ -502,6 +508,8 @@ static int dlpar_memory_remove_by_index(u32 drc_index)
else
pr_debug("Memory at %llx was hot-removed\n", lmb->base_addr);
+ memory_batch_shrink_end();
+
return rc;
}
@@ -532,6 +540,8 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index)
if (lmbs_available < lmbs_to_remove)
return -EINVAL;
+ memory_batch_shrink_begin();
+
for_each_drmem_lmb_in_range(lmb, start_lmb, end_lmb) {
if (!(lmb->flags & DRCONF_MEM_ASSIGNED))
continue;
@@ -572,6 +582,8 @@ static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index)
}
}
+ memory_batch_shrink_end();
+
return rc;
}
@@ -700,6 +712,7 @@ static int dlpar_memory_add_by_count(u32 lmbs_to_add)
if (lmbs_added != lmbs_to_add) {
pr_err("Memory hot-add failed, removing any added LMBs\n");
+ memory_batch_shrink_begin();
for_each_drmem_lmb(lmb) {
if (!drmem_lmb_reserved(lmb))
continue;
@@ -713,6 +726,7 @@ static int dlpar_memory_add_by_count(u32 lmbs_to_add)
drmem_remove_lmb_reservation(lmb);
}
+ memory_batch_shrink_end();
rc = -EINVAL;
} else {
for_each_drmem_lmb(lmb) {
@@ -814,6 +828,7 @@ static int dlpar_memory_add_by_ic(u32 lmbs_to_add, u32 drc_index)
if (rc) {
pr_err("Memory indexed-count-add failed, removing any added LMBs\n");
+ memory_batch_shrink_begin();
for_each_drmem_lmb_in_range(lmb, start_lmb, end_lmb) {
if (!drmem_lmb_reserved(lmb))
continue;
@@ -827,6 +842,7 @@ static int dlpar_memory_add_by_ic(u32 lmbs_to_add, u32 drc_index)
drmem_remove_lmb_reservation(lmb);
}
+ memory_batch_shrink_end();
rc = -EINVAL;
} else {
for_each_drmem_lmb_in_range(lmb, start_lmb, end_lmb) {
--
2.29.2